The present invention relates generally to a system for protecting threads. More particularly, the invention relates to a system for protecting machine threads as well as methods for producing and attaching such protective devices to machine threads.
Threads are found, for example, on machine parts and pipes. Threads typically represent delicate areas that must be protected against harmful mechanical and chemical effects during their transportation and storage.
Consequently, it often becomes necessary to protect machine parts and pipes from damage by using protective caps and the like. When pipes are transported, for example, they are often subjected to very rough treatment. If pipes are to be used in a drilling operation, they are often first pulled up a drilling tower and, as a result, suffer damage. The actual threads, as well as the sealing flanges on the ends of the threads, are often damaged. Even a slightly damaged thread can render an expensive pipe unusable.
In addition to mechanical damage to pipes, the effect of the environment also can render pipes unusable. Salt water, sand, dust, as well as snow, rain, and wind have adverse effects on pipes. Corroded or rusted threads and sealing flanges render pipes unusable; repair of such chemically damaged pipes is expensive. Thus, it is imperative that threads and sealing flanges remain in good condition if the threads are to maintain good connections.
In conventional practice, threads have been protected by screwing protective caps onto them. Such caps may be either open sleeves or closed plugs. Protective caps may be screwed onto the pipes having threads on their outer surface (pivots). Similarly, protective caps may be used which have threads on their exterior surface which are screwed onto the inside threads (bushings) of a pipe.
Protection against chemical influences may be achieved by coating the threads with grease. In addition, there are now protective caps made of synthetic material; such caps often provide sufficient protection for threads.
There are many cases, however, where very high demands are made on the mechanical strength of a protective cap. For example, it is common to pull pipes, which are to be used in an oil drilling operation, into a drilling tower. During such an operation, the lower end of the pipe experiences considerable mechanical stress as a result of the fact that the end of the pipe is dragged on the ground.
Oil drilling operations require that once the pipe is moved into position, the device for protecting the threads must be removed in a very short time. For the steel protective caps now often used, removal is performed by unscrewing the cap. However, this process is time consuming.
In order to reduce the time that is necessary to remove such a steel protective cap, it is frequently loosened before the pipe is pulled onto the drilling tower. Such loosening, however, often causes the protective cap to become cross-threaded such that the thread is damaged by further forced loosening.
Other types of caps are available which are used especially for transporting a pipe onto a drilling tower. Such caps, however, have the disadvantage that they do not sufficiently protect the threads from dirt. Also, such caps often wear out quickly. Moreover, the installation of such a special cap requires time and consequently increases the labor costs of the drilling operation.
Use of steel caps is often undesirable, since they do not protect threads against stronger impacts. Rather, such impacts destroy both the cap and pipe. Furthermore, steel caps often become cross-threaded, and turning the cap then leads to the destruction of the thread. Moreover, steel caps cannot protect threads against the effects of water, moisture, sand, and dust. When pipes are stored for extended periods in the open, the threads thus are exposed to corrosion.
To avoid these disadvantages, pipe users occassionally use protective caps made of metal which are lined with an elastomeric material. The elastomeric material thus provides a better seal between the steel cap and the thread, as well as providing a cushion between the cap and the thread. This helps to protect against the effects of moisture as well as mechanical impact.
It is clear, however, that manufacturing protective caps with an inside lining of elastomeric material requires increased technical expertise as well as added expense. Moreover, such lined caps are ineffective to fully protect threads against moisture, water, and dust.
A type of protective cap currently available is made of synthetic material. Such synthetic caps may be produced with threads; after such caps have been placed on the threads of pipes, they may only be removed by the time-consuming process of unscrewing them. Some synthetic caps do not have threads; this type of construction is also undesirable, since such caps do not fit tightly on the pipes. Thus, the caps are subject to being pulled off inadvertently and do not provide good protection against the penetration of water and dirt.
In order to protect the outer and inner threads of pipes, protective caps, consisting of steel, plastic, or a combination of the materials, are often used. Even if such protective caps are screwed onto the threads and do provide some protection for the threads against damage, such devices provide no protection for the inside of a pipe. As a result, foreign substances, such as water, dirt, ice, and sand, become lodged in the interior of the pipe.
Pipes are often inserted into wells having depths as great as several thousand meters. Thus, a large number of pipes must be screwed together. The threads of the upper pipes must absorb the weight of the entire pipe line. Moreover, the screw connections between the pipes must often be gas-tight. Therefore, complicated thread designs are frequently used. It is clear that such threads must remain intact after their manufacture.
Pipes are also often connected by welding them together. The ends of such pipes are often provided with precise welding chamfers which, like the pipe threads, must be protected.
Pipes used in drilling operations frequently are transported or stored for extended periods. During such times, the pipes are exposed to weather and dirt. If left without protection, the pipe ends are in contact with foreign substances and often corrode, causing a lessening of the integrity of the pipe ends. When such pipes are then to be used, it is a time consuming and expensive task to sort out which pipes are usable.